Catalytic reforming of hydrocarbons in the presence of hydrogen



April 3, 1951 E. T. LAYNG 2,547,221

CATALYTIC REEORMING 0E HYDRocARBoNs 1N TEE PRESENCE oF EYDRoGEN FiledJuly 5, 1947 Patented Apr. 3, 19151 CATALYTIC REFORMIN G 0F HYDROCAB"BONS IN THE PRESENCE OF HYDROGEN Edwin T. Layng, New vYork, N Y.,assigner to The M. W. Kellogg Company, Jersey City, N. J., a

corporation of Delaware Application July 5, 1947, Serial No .759,27 6

In Canada July 26, 1940 12 Claims. l

The present invention relates to the vconversion of aliphatichydrocarbons including acyclic and alicyclic hydrocarbons to aromatichydrocarbons by treatment ,over a suitable catalyst. In one aspect thisinvention relates to the conversion oi hydrocarbon .stocks boilingwithin, and in some cases Within and somewhat above, the .gasolineboiling point range to high-grade motor vfuel by catalytic aromatizationunder critically delined conditions. In another aspect the inventionrelates to `a cyclic conversion process wherein the catalyst is employedin successiveistages .of conversion `and regeneration and wherein thespent catalyst is subjected to an improved vregeneration procedure.

The present application is a continuationfin part of my prior andco-pending applications, Serial No. 376,783, filed January 31, 1941, inwhich I am the sole inventor; and Serial No. 440,762, led April 28,1942, in which I ama co-inventor, both of said applications now beingabandoned. The above-mentioned application .Serial No. 440,762 is adivision of application Serial No. 294,784, liled September r13, 1939,noW Patent No. 2,320,147, issued May 25, 1943. Application Serial No..440,762 particularly relates to a jprocess .for the aromatization ofaliphatic hydrocarbons and discloses specific and criticallcor-iditio'ns .of operation, suitable aromatization catalysts and theircomposition, andthe method of `manu-facturing the catalyst. Referencemayv `be therefore, to application Serial No. 440,762 .orto Patent No.2,320,147 for more specific and -detailed discussion of the{aromatization reaction conditions .and the aromati-Zation catalyst.

In certain of its aspects, the present invention may be regarded as animprovement on the process described in copending vapplication SerialNo. 294,784, filed September 13, 1939, now Patent No. 2,320,147issuedlMayl'25, 19.43, of which the *present applicant is acro-inventor. vPursuant to the A`process described fin said application,"aliphatic hydrocarbons, such as a naphtha of low antiknock rating, "isconverted into Va highlyaromatic motor -fuel of high anti-knock rating"by a catalytic dehydrogenating and cyclicizing reaction. In thisprocess the naphtlfia is passed -in contact with an -aromatizingcatalyst at 'a suitable ele- -vated temperature and space :velocity toeffect the desired conversion, and 'preferably-in the pres ence of'added hydrogen and under asuit'abledevv'gree of superatmosnhericpressure. MlDuring the Aconversion the catalyst is progressivelyldeactivrated by reason of the accumulation of a .ca-r.- vTbonaceousdeposit thereon and, accordingly. its v activity -m-ust be eventuallyrestored by removal of the carbonaceous deposit.

CAB

The usual practice is to regenerate the spentcatalyst by removing thecarbonaceous deposit by combustion, and since the combustion react-ionis strongly `exotherrnic it vmust be effected under carefully controlledconditions and particularly at a temperature notin excess of thecritical terni perature at Which the activity of the catalyst isdestroyed. The complete removal of carbonaceous material is indicated bythe appearance of uncornbined oxygen'in the elliuent regeneration gas.Thereafter, the regenerated catalyst may suitably be purged to f ree ito f regeneration gases, and also reheated to a temperature suitable forthe following hydrocarbon'conversion operation.

It is all Object of this invention to provide na process for theconversion of `aliphatic hydrocarbons to aromatic hydrocarbons. It iS .a.further object `of this invention to provide a process for theconversion of a vstock .boiling approximately Within the gasolineboiling range, and rich lin aliphatic hydrocarbons, into high yields ofahighly aromatic motor fuel. "It is a particularly important object ofthis invention to provide a ,catalytic aromatization process to vproduceextremely small amounts of coke and to give long catalyst life. fIt isstill a further `object of this invention to provide a continuousprocess'for the regenerationcf spent catalyst used in a process for 'reforminghydrocarbons. Other and more .detailed objects, advantages, and uses `ofthis invention Will become apparent ,as description thereof proceeds.

I'have ascertained that the activity .of the catalyst is not restored bysuch regeneration methods ,to an .extent fas large asis desirable, andthe pri.-

. mary object of my .invention is the proyisionof a f active metallic`cormzaonentof the catalyst. Ithas been ascertained'thata substantialenhancement ofthe activityV of the regenerated catalystmay ,be

V,accomplished thereby.

The appended drab/'zing illustrates ,diagrama matieally Ta sui-tablearrangement of `apparatus and process flow for the practice `of theinvention. y

The principal elements of the apparatus g e sa furnace l kfor vaporizingand lheating the hydrocarbon charge, pair of similar reactors or cata.lystchambers Afand Bcontaining a suitable cata.- lyst and manifoldedvwith fluid inlets .and outlets so that each reactor alternately passesthrough the successive steps in the complete reaction and regenerationcycle, and auxiliary regeneration equipment including a compressor 2 forsupplying an oxygen-containing gas, a flue gas producer and heater 3,and a Waste heat boiler 4.

Although not limited thereto, the invention is especially wellexemplified by its application to the conversion of a low anti-knockrating naphtha into an aromatic motor fuel of high anti-knock rating bya procedure such as that described in application Serial No. 294,784,above mentioned. Pursuant to this process, vapors of the naphthaundergoing treatment are passed in contact with a suitabledehydro-aromatization catalyst under conditions adapted to largelydehydrogenate and cyclicize aliphatic compounds present therein tocorresponding aromatic compounds. The catalyst comprises about 6 percent by weight of molybdenum oxide impregnated in or supported onactivated alumina.

The naphtha charging stock comprises an East Texas heavy naphtha havingan A. P. I. gravity of 50.3 containing approximately 14 per centaromatics, 33 per cent naphthenes, and no olens, and the remainder beinglargely paraffin hydrocarbons. This naphtha has an initial boiling pointof about 248 F., a 50 per cent boiling point of about 310 F. and an endpoint of about 396 F. The original octane number measured by theCooperative Fuel Research Motor Method is 42.3 It is contemplated thatthe reaction conditions thus maintained will involve the maintenance ofan average reaction temperature within the range 875 to 1075 F., forexample a temperature of about 975 F., a time factor within the rangebetween 0.1 and 25, preferably between 0.2 and 20, for example a timefactor of one, this factor representing the number of hours required toflow one volume of charge measured on a liquid basis through one volumeof catalyst space, a superatmospheric reaction pressure within the rangeof about to 450 pounds per square inch, preferably 50 to 375 pounds persquare inch, for example a pressure of 315 pounds,

and added hydrogen in amount ranging fromy 0.5 mol to 8 mols ofhydrogen-per mol of naphtha charge, for example 3 mols. Passage of themixture of hydrocarbon vapors and hydrogen over the catalyst under theseconditions is continued until a carbonaceous deposit on the catalystaccumulates to an extent where regeneration of the catalyst by removalof the deposit is necessary or economically desirable. By themaintenance of a superatmospheric pressure Within the above indicatedrange and added hydrogen, the feasible length of the conversion periodbefore regeneration' is greatly extended.

f AAs to the catalyst used in this process, the oxides of the metals ofthe left-hand column of group v VI of the period table, particularlychromium, molybdenum, and tungsten are preu ferred, but other metallicoxides and other metal- 1lic compounds, particularly oxides of themetals of the left-hand group of columns IV and V of the periodic table,such as titanium, cerium, thorium, and vanadium may be used. Moreover,

percentage varies, of course, with the catalyst used. It will also beapparent that mixed catalysts can be used, for instance a mixture ofchromium oxide and molybdenum oxide alone or preferably on an aluminasupport, and in this case the active catalytic oxides should be fromabout 1 to about 25 per cent by weight of the total catalyst. Anothercatalyst which can be used is magnesium chromite either alone or on asuitable support, preferably alumina. In fact, any aromatizationcatalyst or metal which promotes dehydrogenation and cyclization ofaliphatic hydrocarbons can be used. As those skilled in the art know,the efciency of a given catalyst is largely determined by its method ofpreparation, and consequently some catalysts give better results thanothers under specific conditions. For a detailed description of themethod of preparation of the catalyst, reference may be had to myco-pending application, Serial No. 440,762, or my Patent No. 2,320,147,of which the present application is a continuation-in-part. Of all ofthe catalysts I prefer Vto use a catalyst comprising molybdenum oxidesupported on alumina, particularly activated alumina, and the molybdenumoxide should most advantageously constitute from about 2 to about 10 percent by weight of the total catalyst since this has been found toinclude a sharpV optimum which gives best results. Larger amounts ofmolybdenum oxide can, however, be used.

I prefer that the catalyst be substantially free from sulphur sincesulphide catalyst as contrasted with oxide catalyst tends to degrade thestock to less valuable parafiin and lead to dominant hydrogenationrather than predominant dehydrogenation, i. e., hydrogen consumptionrather than hydrogen production. These hydrogen sulphides also result inincreased production As previously indicated the oxide catalysts arepreferred but in some cases, such as the preferred molybdenum oxidecatalyst, the oxide tends to be reduced inthe process and in generalinstead of using the oxides of the metals of the left-hand columns ofgroups IV, V, VI, the metals themselves can be used, preferablysupported on alumina.

The present process may be applied to various feed stocks, for example aMichigan virgin naphtha having an A. P. I. gravity of 61.5. This naphthahas an initial boiling point of 129 F., a

per cent boiling point of 270 F., and an endv point of 396 F., and anoctane number of 24. Another example of a charging stock is a Californiavirgin naphtha having an A. P. I. gravity of 47.0, containing 1.5 percent olefins and 13.5 per cent aromatics. This naphtha has.v an initialboiling point of 258 F., a 50 per centboiling point of 305- F., and anend point of 398 F., and an octane number of 57.8.

The productl of the present invention has a high aromatic content withsubstantially small amounts of clens. The A. P. I. gravity of theproduct is' a good measure of its content of while these catalyticoxides can be used alone on various supports including magnesia, I findit very highly preferable to utilize them on alumina, particularly anactivated alumina or on 'alumina gel as a support, and in general thecatalytic oxides or other catalytic compounds should be the minorconstituents, usually from 1 to 40 per cent by weight of the totalcatalyst including thersupport, although the optimum aromatichydrocarbons since aromatics having low A. P. I. gravity or, in otherwords, high specific gravities. The A. P. I. gravity of the product mayvary between 50 and about 40 degrees. With increasing octane number thegravity of theproduct tends to drop off. The gravity of the stabilizedproduct is less than, and for the preferred operating conditions,atleast 3 A. P. I. less than, the gravity of that part of the originalcharge stock rhaving the same end point as the endpoint of the product.

Regeneration of the catalyst is most suitably effected by removing thecarbonaceous deposit by combustion. During thisoperation carefultemperature control is necessary in order to burn oi the carbonaceousmaterial at a suitable rate andat the same time prevent permanentimpair- Yment or destruction of the catalysts activity which resultsfrom excessively high temperatures. Such temperatures may be avoided byremoving the exothermic heat of combustion vat a suitable rate, effectedusually either by indirect heat exchange with cooling coils or similarcooling suriv faces embedded in the catalyst, or by the circulaf tionofan inert gas -such as i'lue vgas with the roxidizing medium, such asair.

tween these steps is normally required. In addi tion, purging of theresidue gases or vapors, and adjustment of the temperature 4of thecatalyst during the periods intervening between the reaction andregeneration operations is usually desirable. The present inventioncontemplates an additional intervening treatment whereby the yactivityof the spent catalyst and its suitability for reuse is substantiallyenhanced com-pared with the results obtained by removal of thecarbonaceous deposit alone. The complete process may suitably involvethe steps enumerated below, i-t being understood that certain of thesesteps may be omitted and other steps`added without departing from `theessential features of the inlvention':

, V1.-Reaction or on-stream operation .2.,--Depressuring 3.-'-Purging4.--Repressuring 5.-Regeneration, or .combustion of the deposit6.-Oxidation of the .catalyst 'If-Reheating 8.-Depressuring 9.--Purging1,0.-Repressuring During the reaction or on-streani vperiod a mixedstream of heated vnaplfitha vapors and 'hydrogen is supplied to theparticular reactor onstream through reactants inlet valve 5a Aor 5b andpassed therethrough in intimate contact with the catalyst which isdisposed .in "the're'actor in the form of a bed resting on a suitableperforated support or in any other suitable manner. 'ns previouslyindicated, catalysts comprising an oxide of vanadium or a'metal from thegroup forming the .left-hand column of group VI of the `periodic tableare greatly preferred, particularly molybdenum oxide, preferablysupported on activated Y alumina.

'Chromium catalysts vcan also be used 'in place'of molybdenum catalysts,V`particularly Icatalysts containing from 1:5 to i0 per cent Cr2O3' byWeight Aon alumina. A catalyst'containing '25 percent "superatmosphericpressure.

-ablow-down stack (not shown).

Crz'Oa `on 75 per cent of activated aluminaisan example. The method vofpreparation .of this catalyst is disclosed in my copending application,Serial No. 440,762, and my Patent No. 2,320,147, above referred to.

The hydrogen gas mixed with the charge may suitably consist of a recyclegas derived from gas separator 5 which contains a large amount oihydrogen in mixture with normally gaseous hydrocarbons. The recycle gasand naphtha charge are supplied to a suitable heating means such asfurnace I by Ylines 'I and 8, respectively, and the heated products arewithdrawn from the heater by lines 9 and lil, respectively, and passedto the reactor inlet manifold Il. The specific arrangement shown has theadvantage of supplying a substantial amount of the heat of reaction byvmeans of the heated recycle gas and the admixture of 'the recycle gasat a point immediately prior to the introduction into the reactormanifold assists in vavoiding undesirable thermal decomposition. Thevaporous7 conversion products are withdrawn through valves I2a or I2band pass to reactor products transfer line VI 3 to a condenser I4wherein normallyv liquid constituents are condensed, and the cooledmixture passed by -line I6 to gas separator 6, wherein a gaseousfraction including the recycle gas is withdrawn 4overhead through lineil, and the liquid products withdrawn from the bottom through line i8and pumped by pump l@ to asuitable products recov- Very system such as afractionator, rerun tower and the like. Net make hydrogen gas isWithdrawn through line 23 `controlled by valve 2l which valve controlsthe pressure imposed on the reaction system. The recycle gas fraction iswithdrawn through line 22 and compressed by vcompressor 23 to thepressure necessary to force it through heater l and reintroduced intothe reaction system.

The regeneration equipment includes a suitable means such as a wasteheat boiler 4 for cooling and recovering energy from the elluent hotregeneration gas and lowering its temperature to that suitable forrecirculating t'o the reactor. In order that steam production in boiler4 may be `suitably constant a iiue `vgas producer and heater 3 Visprovided from which flue gas may be passed either directly to thereactor or by way of 'Dy-pass line l25 to boiler'4. Blower 56 inline 24yis preferably 4operated in such a manner as vto circulate through line-24 flue gas at a constant rate at Yall times and under a suitabledegree of Dependent upon the lrequirements of the system, device 3 maybe oper- Vated merely as a mixer for flue gas and air, or as a hot fluegas producer by admitting air and fuel vgas through valves 31 and 38 tothe burner 30.

As a starting point in considering the regeneration procedure, reactor Amay be regarded as being at the point where it is just completing re-laction and is ready for regeneration, the oil inlet and outlet valves5a, '42a being openand all other valves closed. During this time the uegas 'is being recirculated through lines 24, 25, 26, 21 and 28,completely by-passing both reactors, and is heated in the flue gasheater 3 by combustion of fuel gas and air Vin burner 3Q and isthereafter cooled in waste heat boiler 4. The first step in theregeneration procedure 1i the preparation for purging by depress'uringthe reactor Yto atmospheric pressure. This is effected by closing theoil vapor 'inlet valve 5a and oil outlet valve 12a and opening Valve 31aleading lto The oil vapors Yeration temperature.

Vprogresses.

then pass into the blow-down stack in a period of a few minutes, thedepressuring rate being controlled in order to prevent damage to thecatalyst and supporting structure.

The next operation is to purge residual oil vapors from the reactor bypassing an inert gas through the reactor. This may be suitablyaccomplished by bleeding excess flue gas from the recirculating systeminto the reactor through valve 32a., the rate preferablyb-eingrcontrolled by a back pressure controller 33 to maintain pressureon the recirculating system substantially constant. This operation iscontinued until a suitable volume of the purging medium, for exampleabout luvolumes, has been passed through the reactor, at which timevalve 3 la is closed and the reactor is repressured with flue gas to thepressure of the circulatingsystem, for example about 50 or 100 pounds,by continuing to admit flue gas to the chambers through valve 32a.

When the pressure in the chambers has reached the pressure of thecirculating system, valve 32a is closed and valves 34d and 35a areopened, allowing the recirculating flue gas to pass through the reactor.Immediately thereafter Valve 3S admitting coke combustion air to thesystem is opened and valves 3l and 3B are closed thereby cutting off thecombustible gas mixture and the heat supply from the iiue gas burner 3.The flue gas and air mixture at a relatively low temperature above theignition temperature, between about `600" F. and about '775 F., forexample about 650 F., is now flowing through reactor A causingcombustion of coke therein, the resulting heat being removed in wasteheat boiler 4, the hot combustion gas passing thereto through lines 39,40, and 2E. The quantity of oxygen or air thus introduced is regulatedin such manner that the combustion will proceed at a suitable ratewithout exceeding the safe maximum regen- The oxygen content of the iuegas and air mixture entering the reactor is usually about l to about 2per cent. The burning occurs in a relatively narrow horizontal band Aorzone which starts at the place of injection of the flue gas and airmixture into the catalyst bed and moves down through the bed asregeneration The heat liberated by this burning is adsorbed as sensibleheat in the flue gas which is heated from its relatively low initialtemperature to a temperature of about 1l50 F., the latter representingthe maximum safe regeneration temperature. the carbonaceous deposit orcoke the catalyst bed is left at a temperature approximating thetemperature of the cooled recirculated flue gas.

presence of uncombined oxygen in the eiiiuent gas.

At this stage pursuant to the present invention, the circulated nue gasis preferably heated to a higher temperature than in the first stageregeneration by burning a mixture of fuel gas and air introduced throughvalves 37 and 38 to vburner 30, and at the same time excess air isintroduced through valve 35 into the heated mixture. The resultingtemperature of the gaseous mixture is at least 25 F. above the flue gasin the first stage regeneration, generally at a temperature of about 750F. to about 859 F. or higher` Preferably the temperature of the flue gasin the second stage should be at least 800 F. The hot oxidizing gas thusproduced passes through the reactor for a sufficient period to sub-Ystantially completely oxidize the active metallic After completion ofcombustion of f is shut off by closing air valve 3S.

component of the catalyst and to burn any remaining or embeddedcarbonaceous deposits. For example, in the case of a catalyst comprisingmolybdenum, this is oxidized entirely or substantially entirely to theform of the trioxide. The maximum safe temperature during the secondregeneration or oxidizaton step is about 1150 F. similar to the maximumsafe regeneration temperature of the rst regeneration step in order toprevent injury to the catalyst. The oxygen content of the ue gas and airmixture is controlled to Vbe the same or less than the oxygen contento-f the flue gas mixture in the first regeneration step in order toprevent the aforesaid maximum safe temperature from being exceededAduring the second regeneration or oxidation step. Preferably, theoxygen content of the ue gas mixture in the second stage is held belowabout l per cent by controlling the amount of excess air introducedthrough valve 35 in order to prevent overheating of the catalyst in thesecond regeneration step which uses a higher inlet temperature of thehot oxidizing gas.

The advantage of eiecting the second stage of the regeneration oroxidization at a higher inlet temperature of the flue gas than in thefirst stage is not only that the active metallic components may becompletely oxidized and embedded carbonaceous deposits burned, but atthe higher inlet temperatures the reaction rate is greatly increased;for example, the reaction rate may be increased as much as 2 or 3 timesthe reaction rate at lower inlet temperatures. Increased reaction ratesshorten the time required for regeneration and make for an overall moreeiiicient regeneration system.

Upon completion of the foregoing second regeneratio-n or catalystoxidation step, the temperature of the catalyst may still be somewhatbelow the normally desired conversion temperature. In order to reheatthe catalyst to this temperature, the supply of heat to the recirculatedue gas is continued by burning fuel gas and air in the burner` 36 butthe supply of excess oxygen The temperature of the flue gas suppliedfrom iiue gas heater 3 at this time is relatively high, for exampleabout 1075 F. While the temperature of the flue gas from the reactorremains at a relatively low temperature for a substantial portion of thereheating period. This may necessitate oy-passing a portion of it aroundthe waste heat boiler by line 4| in order not to reduce the temperatureof the flue gas to the flue gas circulating line 24 below h the desiredminimum, the flow through the by- T e completion of this combustion isevidenced by the pass being controlled by a temperature controller (notshown). The reheating operation is continued until suicient heat hasbeen imparted to the catalyst bed to raise the average temperaturethereof to the desired reaction temperature at which time flue gasby-pass valve 12in line 25 is opened, andvalves Sta and 35a are closed.l

Depressuring of the reactor is now .effected by opening valve Slaconveying the iue gas to the blow-down stack. Valve 3m may then beclosed and the reactor is then purged and repressured with recycle gasadmitted through valve 43a t o the desiredreaction pressure, for exampleabout 315 lbs. When the pressure on the reactor reaches therequiredpressure the fiow of the repressuring gas is stopped by closingvalve 43a. In a desirable modification of the step, in place of closingvalve Sla prior to the admission of recycle gas this valve is permittedto remain open and recycled gasis passed'throughthe reactor' there- 3.byveiecting a partial reduction of the." catalyst and enhancing itsactivity as set forth in my cpending application Serial No. 294,785,filed onV September 13, 1939, now Patent, No. 2,270,715. Such-v areduction is effected to a certain extent by. repressuring alone sincethis operation is preferably effected over a substantial period of timeand at the rate at which make hydrogen gasv is available.

ReactorA now contains recycle gas at the required reaction pressure andis ready to be placed in reactor service. in place of reactor B whichhas at'this point reachedfthe end of the reaction cycle. Reactor A isnow put on reaction by opening valve a and I2a and reactor B. is removedfrom reaction by closing the corresponding valves on it, thus completingthe regeneration steps in reactor A.

AIt is to be. understood that the time required for the variousoperations is susceptible to substantial variations dependent upon suchfactors asv the character of the charging stock, degree of conversionand the like. As an example of the general magnitude ofY the. timesuitably utilized for the various steps reference is made to theconversion by the procedure above described of a heavy virgin East Texasnaphtha having an A. P. I. gravity of 51.2 and an octane number of 45.3to a highly aromatic reformate having a gravity of 49 and an octanenumber of 80.0. In this instance a. twelve hour cycle period wasemployed, each reactor being ori-stream for a period. of six hours, andengaged in theY various steps of the regeneration procedure for theremaining six hours. In this particular regeneration procedure, a periodof about four and a half hours was utilized for combustion of thecarbonaceous deposit, a period of about fortyminutes for oxidation ofthe catalyst, a period of about twenty minutes for the Yreheating step,a period of about twenty minutes forthe step of repressuring andtreatment. with recycle gas, and the remaining time was distributed overthe -other operations and necessary time for valve changes.

. The substantial completion of the coke combustion step isl indicatedby the oxygen .and carbon dioxide content of the effluent gas from thisstage. Completion of coke combustion is indicated when no furtherincrease in the carbon dioxide content of the efliuent gas occurs andfree oxygen appears therein. Completion of the catalyst oxidation orsecond stage regeneration step is indicated. at the point where the freeoxygen content 4of the efliuent gases is the same as that of theentering gases and also by the point at whichheat evolution due to theexothermic reaction involved ceases. It is to be understood that tracesof residual carbonaceous material may be burned off 'during the catalystoxidation step; It will also be apparent that the specific apparatus andprocess iiow above described is merely exemplary of my invention, andvarious other forms of apparatus and process fiow may be advantageouslyutilized with certain types of charging stock. For example, in theconversion ,of cracked naphthas containing high amounts of' sulphur,apparatus and process flow such as set forth in my copending applicationSerial No.`

358,750, filed September 28, 1940, and abandoned October 29, 1945, maybe utilized to advantage. In the latter' type of apparatus four or moretypes of reactorchambers are employed and one chamber is engaged in cokecombustion at all times during the reaction, hence it is feasible todispensey with a ue gas heater and producer except during the startingup period. These and various other possible modifications in applying myinvention will bev apparent to those skilled in the art and it is to beunderstood that its scope is not limited otherwise than is required bythe, claims appended hereto.

I claim:

l. The method of reforming a hydrocarbon in the presence of a catalystwhich, consistsy essentially of a reducible metal oxide of group VI ofthe periodic system carried on an aluminacontaining base and added freehydrogen in which operation the reaction takes place undersuperatmospheric.. pressure and which operation requires periodicregeneration of the catalyst, the improvement which comprises subjectingthe catalyst after regeneration to a purging operation with freehydrogen or free hydrogen-containing gas carried out at pressuressubstantially less than those employedd-uring the said reformingoperation.

2. The method of producing an aromatic from a hydrocarbon. fractioncontaining a naphthene which comprises contacting the said feed stockwith a reforming catalyst consisting essentially of a reducible metaloxide selected from the class consisting of molybdenum oxide andchromium oxide carried on an alumina support, in the presence of addedfree. hydrogen and under reforming conditions of temperature andpressure, withdrawing reaction products, discontinuing .the flow of feedstock to the catalyst, regenerating the catalyst, purging with inert gasand-prior to returning the feed stock to the catalyst, purging the saidcatalyst with a free hydrogen-con'- taining gas at pressuressubstantially below those employed during the reforming operation.

3. The method vset forth in claim. 2 in which catalyst is purged with aiiue gas at pressures prevailing during the reforming operation andthereafter purged with a free hydrogen-containing gas at pressuressubstantially below those employed during the reforming operation.

4,. The method set forth in claim 2 in which following purging with afree hydrogen-containing gas at reduced pressures the system isrepressured with a gas containing hydrogen.

5. The method of reforming a hydrocarbon which comprises contacting ahydrocarbon feed with a reforming catalyst consisting essentially of areducible metal oxide selected from the class consisting of molybdenumoxide and chromium oxide carried on an alumina support, in the pres,-ence of free hydrogen and under reforming conditions of temperature andpressure, withdrawing reaction products, discontinuing the now ofhydrocarbon feed to theA catalyst, regenerating the catalyst, purgingwith inert gas and prior to returning the hydrocarbon feed to thecatalyst, purging the said catalyst with a free hydrogencontaining gasat pressures substantially below those employed during the reformingoperation.

6. The method of claim 5 in which said regeneration operation comprisesthe steps of introducing a mixture of air and iiue gas into contact withthe catalyst at a temperature above the ignition temperature of thecarbonaceous deposits deposited thereon during the reforming operationuntil substantially complete removal of the carbonaceous deposits iseffected and the catalyst is left at a temperature approximating saidinitial introduction temperature, maintaining a maximum saferegeneration temperature below about l F;, subsequently heating anoxygen'- containing. gas to a temperature at least 25 F. higher than thetemperature of the ue gas and 11 air inthe prior stepr of regeneration,and introducing the thus heated oxygen-containing gas into contact withthe catalyst to substantially completely oxidize the active metalliccomponent of the catalyst and burn any remaining carbonaceous depositsthereon.

7. The method according to claim 6 in which the temperature of the airand ue gas in the primary regeneration step is between about 600 F. andabout 775 F. and the temperature of the oxygen-containing gas of thesubsequent step is at least 800 F. i 8. The method of claim 7 in whichfollowing purging with a free hydrogen-containing gas at reducedpressures the system is repressured with a gas containing hydrogen.

9. The method of claim 7 in which catalyst is purged with a flue gas atpressures Vprevailing during the reforming operation and thereafterpurged with a free hydrogen-containing gas at pressures substantiallybelow those employed during the reforming operation.

10. In the method of reforming a hydrocarbon in the presence of acatalyst which consists essentially of a reducible metal oxide of groupVI of the periodic system carried on an aluminacontaining base and addedfree hydrogen in which operation the reaction takes place undersuperatmospheric pressure accompanied by the deposition of carbonaceousdeposits on the catalyst and which operation requires periodicregeneration of the catalyst at a temperature substantially lower thanthe maximum safe regeneration temperature by` introducing a mixture ofair and flue gas into contact with the catalyst at a temperature abovethe ignition temperature of the carbonaceous deposits untilsubstantially complete removal of the carbonaceous deposits is effected,the improvement which comprises heating an oxygen-containing gas afterregeneration of said catalyst to a temperature higher than thetemperature of the oxygen-containing gas used in the aforesaidregeneration and introducing said thus heated oxygen-containing gas intocontact with the catalyst to substantially completely oxidize the activemetallic components of the catalyst and to burn any remainingcarbonaceous deposits, and subsequently subjecting the catalyst afterthe aforesaid oxidation treatment to a purging operation with freehydrogen or free hydrogen-containing gas carried out at pressuresubstantially less than those employed during said reforming operation.

11. In the method of reforming a normally liquid hydrocarbon oil lcontaining naphthenic components in which such a hydrocarbon oil isreformed under superatmospheric pressure and elevated temperatures andin the presence of added free hydrogen and a reforming catalystconsisting essentially of a reducible metalV oxide selected from theclass consisting of molybdenum oxide and chromium oxide carried on analumina support, and in which the catalyst is regenerated by introducingan oxygen-containing gas into contact with said catalyst at atemperature within the range of about 600 F. to about 775 F. untilsubstantially complete removal of carbonaceous material depositedthereon during the reforming operation is effected at a temperaturebelow the maximum safe regeneration temperature, the improvement whichcomprises following said regeneration heatingy an oxygen-containing gasto a temperature in excess of about 800 F. and introducing the thusheated oxygen-containing gas into contact with the catalyst tosubstantially completely oxidize the active metallic component of thecatalyst and burn any remaining carbonaceous material thereon,subsequently purging the catalyst following the aforesaid catalystoxidation treatment with a free hydrogen-containing gas at pressuressubstantially below those employed during the reforming operation.

12. In a process for the conversion of ali-' phatic hydrocarbons toaromatic hydrocarbons involving passing vapors of aliphatic hydrocarbonsinto contact with a metallic oxide aromatizing contact catalyst at anelevated temperature of about 875 F. to about 1075 F. in the presence ofabout 0.4 to about 8 mols of hydrogen per mol of hydrocarbon feed and ata pressure of about 30 to about 450 pounds per square inch, continuingthe passage of said vapors until activity of the catalyst issubstantially decreased by the accumulation of carbonaceous depositsthereon, regenerating the catalyst by introducing a gas containingbetween about l and about 2 per cent oxygen in contact with saidcatalyst at a temperature within the range of 600 to about 775 F. untilsubstantially complete removal of the carbonaceous deposits is effected,

maintaining the temperature of regeneration below the maximum saferegeneration temperature of about 1150 F., and reusing the regeneratedcatalyst for the conversion of further quantities of aliphatichydrocarbons, the improved method of reconditioning said regeneratedcatalyst prior to reuse thereof 'for further conversion which comprisesheating an oxygen-containing gas containing less than 1 per cent oxygento a temperature in excess of about 800 F. and introducing the thusheated oxygen-containing gas into contact with the regenerated catalystto substantially completely oxidize the active metallic componentthereof and to burn any remaining carbonaceous deposits thereon at atemperature below the aforesaid maximum safe regeneration temperature,subsequently purging the catalyst with free hydrogen or freehydrogen-containing gas at a pressure substantially less than thoseemployed during said conversion operation. Y f

EDWIN T. LAYNG.

REFERENCES CITED The following references are of record in the le ofthis patent:

` UNITED STATES PATENTS

1. THE METHOD OF REFORMING A HYDROCARBON IN THE PRESENCE OF A CATALYSTWHICH CONSISTS ESSENTIALLY OF A REDUCIBLE METAL OXIDE OF GROUP VI OF THEPERIODIC SYSTEM CARRIED ON AN ALUMINACONTAINING BASE AND ADDED FREEHYDROGEN IN WHICH OPERATION THE REACTION TAKES PLACE UNDERSUPERATMOSPHERIC PRESSURE AND WHICH OPERATION REQUIRES PERIODICREGENERATION OF THE CATALYST, THE IMPROVEMENT WHICH COMPRISES SUBJECTINGTHE CATALYST AFTER REGENERATION TO A PURGING OPERATION WITH FREEHYDROGEN OR FREE HYDROGEN-CONTAINING